Questions About Supervolcanoes

What is a supervolcano?

Comparison of eruption sizes using the volume of magma erupted from several volcanoes.

The term "supervolcano" implies a volcanic center that has had an eruption of magnitude 8 on the
Volcano Explosivity Index (VEI), meaning
the measured deposits for that eruption is greater than 1,000 cubic kilometers (240 cubic miles).
The
VEI scale was created as a general
measurement of the explosivity of an eruption. There are multiple characteristics used to give an
eruption its VEI allowing for the
classification of current and historic eruptions. The most common criteria are volume of ejecta
(ash,
pumice, lava) and column height.
All VEI 8 eruptions occurred tens of thousands to millions of years ago making the volume of
ejecta or
deposits the best method for
classification. An eruption is classified as a VEI 8 if the measured volume of deposits is greater
than
1,000 cubic kilometers (240 cubic
miles). Therefore a supervolcano is a volcano that at one point in time erupted more than 1,000
cubic
kilometers of deposits.
Yellowstone, like many other supervolcanoes, has also had much smaller eruptions. The cartoon
shows
a comparison of eruption sizes,
including the three largest from Yellowstone. Click on the image for a more detailed description
and
larger view.

What are some other examples of supervolcanoes?

Volcanoes that produced exceedingly voluminous pyroclastic eruptions and formed large calderas
in the
past 2 million years would include
Yellowstone, Long Valley in eastern California, Toba in Indonesia, and Taupo in New Zealand.
Other
"supervolcanoes" would likely include
the large caldera volcanoes of Japan, Indonesia, and South America. The most recent
supervolcanic
eruption on Earth occurred 27,000 years
ago at Taupo located at the center of New Zealand's north island.

I read that scientists couldn't find the Yellowstone caldera until they looked at a photo of
Yellowstone from space. Is this
true?

Not according to Bob Christiansen. Bob is the USGS scientist who delineated the three Yellowstone
calderas and told the world about the
great eruptions that formed them. Bob reports that he traced out the caldera boundaries through
old
fashioned field work... walking
around with a hammer and hand lens and looking carefully at the rocks and their distributions.
Most of
the key observations were made in
the 1960s and 1970s. Several authors have written that these large calderas were discovered from
space
and we suspect that the rumor
probably got started because initial field work that delineated them was partly funded by NASA.
The
idea was to compare well-constrained
geologic maps with images taken from space. So Bob's geologic map was used to verify the NASA
images, not the other way around.

In 2005, BBC and
the Discovery
Channel
produced a docudrama and documentary about
Yellowstone called Supervolcano. Below, Yellowstone Volcano Observatory scientists
answer
questions that arose after this program
aired that relate to supervolcanoes, volcanic hazards, and Yellowstone.

The docudrama Supervolcano dramatically explores the impact of a large caldera-forming
eruption at
Yellowstone. The scale of the
portrayed eruption is similar to the eruption of the Huckleberry Ridge Tuff at Yellowstone 2.1
million
years ago. The movie is realistic
insofar as depicting what could happen if an eruption of this magnitude were to occur again.
Although
the drama is set in the future, it
does an acceptable job of addressing some of the issues scientists would grapple with if
Yellowstone
showed signs of an impending
eruption. The questions and answers below shed light on issues related to volcanism at
Yellowstone. A
much more detailed discussion,
including full-color illustrations, can be found in the
U.S. Geological Survey Fact Sheet
about Yellowstone's activity.

QUESTION: What is the chance of another catastrophic volcanic eruption at Yellowstone?
ANSWER: Although it is possible, scientists are not convinced that there will ever be another
catastrophic eruption at Yellowstone.
Given Yellowstone's past history, the yearly probability of another caldera-forming eruption can be approximated as 1 in 730,000 or
0.00014%. However, this number is based simply on averaging the two intervals between the
three
major past eruptions at Yellowstone
— this is hardly enough to make a critical judgment. This probability is roughly similar to
that of
a large (1 kilometer) asteroid
hitting the Earth. Moreover, catastrophic geologic events are neither regular nor predictable.

QUESTION: What would happen if a "supervolcano" eruption occurred again at Yellowstone?
ANSWER: Such a giant eruption would have regional effects such as falling ash and short-
term
(years to decades) changes to global
climate. The surrounding states of Montana, Idaho, and Wyoming would be affected, as well as
other
places in the United States and the
world. Such eruptions usually form calderas, broad volcanic depressions created as the ground
surface
collapses as a result of
withdrawal of partially molten rock (magma) below. Fortunately, the chances of this sort of
eruption at
Yellowstone are exceedingly
small in the next few thousands of years.

QUESTION: Is Yellowstone monitored for volcanic activity?
ANSWER: Yes. The Yellowstone Volcano Observatory (YVO), a partnership between the United
States Geological Survey (USGS),
Yellowstone National Park, and the University of Utah, closely monitors volcanic activity at
Yellowstone.
The YVO websitefeatures real-
time
data for earthquakes, ground
deformation, stream flow, and selected stream temperatures. In addition, YVO scientists
collaborate
with scientists from around the
world to study the Yellowstone volcano.

QUESTION: Do scientists know if a catastrophic eruption is currently imminent at
Yellowstone?
ANSWER: There is no evidence that a catastrophic eruption at Yellowstone is imminent, and
such
events are unlikely to occur in the
next few centuries. Scientists have also found no indication of an imminent smaller eruption of
lava.

QUESTION: How far in advance could scientists predict an eruption of the Yellowstone
volcano?
ANSWER: The science of forecasting a volcanic eruption has significantly advanced over the
past 25
years. Most scientists think that
the buildup preceding a catastrophic eruption would be detectable for weeks and perhaps months
to
years. Precursors to volcanic eruptions
include strong earthquake swarms and rapid ground deformation and typically take place days to
weeks
before an actual eruption.
Scientists at the Yellowstone Volcano Observatory (YVO) closely monitor the Yellowstone region
for such
precursors. They expect that the
buildup to larger eruptions would include intense precursory activity (far exceeding background
levels)
at multiple spots within the
Yellowstone volcano. As at many caldera systems around the world, small earthquakes, ground
uplift
and subsidence, and gas releases at
Yellowstone are commonplace events and do not reflect impending eruptions.

QUESTION: Can you release some of the pressure at Yellowstone by drilling into the volcano?
ANSWER: No. Scientists agree that drilling into a volcano would be of
questionable usefulness. Notwithstanding the enormous expense and technological
difficulties in drilling through hot, mushy rock, drilling is unlikely
to have much effect. At near magmatic temperatures and pressures, any hole would rapidly
become
sealed by minerals crystallizing from the
natural fluids that are present at those depths.

QUESTION: Could the Yellowstone volcano have an eruption that is not catastrophic?
ANSWER: Yes. Over the past 640,000 years since the last giant eruption at Yellowstone,
approximately 80 relatively nonexplosive
eruptions have occurred and produced primarily lava flows. This would be the most likely kind of
future
eruption. If such an event were
to occur today, there would be much disruption of activities in Yellowstone National Park, but in
all
likelihood few lives would be
threatened. The most recent volcanic eruption at Yellowstone, a lava flow on the Pitchstone
Plateau,
occurred 70,000 years ago.

QUESTION: Because Yellowstone is so geologically active, are there other potential geologic
hazards in Yellowstone?
ANSWER: The heat and geologic forces fueling the massive Yellowstone volcano affect the park in
many
ways. Yellowstone's many geysers,
hotsprings, steam vents, and mudpots are evidence of the heat and geologic forces. These
hydrothermal
(hot water) features are mostly
benign, but can rarely be the sites of violent steam explosions and pose a hydrothermal hazard.
Earthquakes, another example of active
geologic forces, are quite common in Yellowstone, with 1,000 to 3,000 occurring annually. Most
of
these are quite small, although
significant earthquakes have shaken Yellowstone, such as the 1959 magnitude 7.5 Hebgen Lake
quake,
the largest historical earthquake in
the intermountain region, and the 1975 magnitude 6.1 quake near Norris Geyser Basin. The many
earthquakes and steam explosions in the
past 10,000 years at Yellowstone have not led to volcanic eruptions.